1. Field of the Invention
The present invention relates generally to fault detection and restoration in a unidirectional path switched ring network.
2. Description of Background Art
Unidirectional path switched ring (UPSR) optical networks are of interest for telecommunications. Referring to FIG. 1, in a conventional UPSR network 100, a plurality of optical add drop multiplexer (ADM) nodes are coupled into a ring topology by a plurality of working fibers 110 and protection fibers 115. In a UPSR network traffic added at a source node is simultaneously sent on both the working and protection fibers to a destination node (also sometimes known as the “receiving node”). The two versions of the traffic are sent along opposite ring directions, e.g., in FIG. 1 traffic between nodes A and node B may be sent clockwise on the working fibers or counterclockwise on the protection fibers. The destination node selects the better version of the signal, which is coupled to the tributary network. Commonly, the default rule is that the working path signal is coupled to the tributary network unless a loss of signal or signal degradation is detected from the working path signal received by the destination node.
Some standard protocols permit alarm signals to be used to propagate fault information. For example, the synchronous digital hierarchy (SDH) and synchronous optical network (SONET) standards include alarm signal protocols. SONET, for example, includes an alarm indication signal (AIS), such as an alarm indication signal line (AIS-L), generated to replace a normal traffic signal when the traffic contains a defect condition, such as a loss of signal (LOS), loss of frame (LOF), or other form of degradation. The AIS notifies downstream devices of an upstream defect condition. This is particularly useful if signal degradation occurs at a tributary interface where the signal enters a source node. Similarly, SDH includes alarm signal protocols, such as a multiplexer section alarm indication signal MS-AIS.
However, some types of services do not have standard alarm signal protocols comparable to the AIS or MS-AIS. These include, for example, Gigabit Ethernet, Fiber Channel, and Clear Channel, for which there are no corresponding alarm signal protocol such as an AIS for forwarding fault information. Consequently, network performance may be deleteriously affected.
What is desired is a new system and method for forwarding fault information in an optical network.
The figures depict a preferred embodiment of the present invention for purposes of illustration only. One of skill in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods disclosed herein may be employed without departing from the principles of the claimed invention.